Traditional operative orthognathic surgery involves cutting (osteotomizing) a skeletal structure of an upper and/or lower jaw (maxilla and mandible), repositioning the osteotomized dentate skeletal segments with teeth into pre-operatively determined positions, and then fixing the mobile dentate skeletal jaw segments into the pre-determined position with a combination of wires, plates, and screws (rigid fixation) and inter-maxillary fixation (wiring teeth together).
Once the jaw(s) are cut (osteotomized) the dentate skeletal segments are loose and lose a positional relationship relative to each other and to a remaining stable, uncut, facial skeleton. One challenge of successful orthognathic surgery is determining where to position and fix the osteotomized dentate skeletal segments with respect to the remaining, uncut facial skeleton.
Typically, preoperative planning is utilized to predict required changes to the original position of the teeth and jaws of the patient. Anticipated changes to dentate skeletal segments in orthognathic surgery can be determined through various documented methodologies including clinical evaluation of the patient's face and head, cephalometric x-rays, photographs, and through dental models mounted on a dental articulator. More accurately, pre-surgical planning in a digital environment can be performed using computed tomography (e.g. CT/CBCT) and a laser dental (occlusal) scan. Regardless of the methodology utilized in a pre-operative planning, there is currently no accurate technique for translating planned skeletal movements to intra-operative stable skeletal reference points or landmarks.
Intra-operative surgical occlusal splints are important traditional devices for determining the relationship of the teeth of the upper and lower jaws during orthognathic surgery. The occlusal surgical splints can be manufactured from computed tomography and digital dental models or from traditional plaster dental models. Regardless of how dental occlusal splints are manufactured, the splints secure only changes in dental relationships, thereby providing no reference for final intra-operative repositioning of the dentate skeletal segments relative to the uncut facial skeleton. While splints assist in determining changes in dental or occlusal relationships, lacking is a method to precisely determine the final skeletal position of the osteotomized dentate skeletal segments in orthognathic surgery.
Specifically, when a dentate skeletal segment of the face is cut or osteotomized, the loose mobile skeletal segment must be related back to a stable (uncut) facial skeleton assuming a final post-osteotomy position. For example, in the most common orthognathic procedure performed, LeFort I maxillary osteotomy, (horizontal cut across the maxilla at the approximate level of the nasal floor) following completion of the upper jaw transverse cut or osteotomy, the dentate skeletal segment is loose or mobile.
Traditionally, the mobile maxillary (LeFort I) dentate skeleton segment is related to the uncut lower jaw or mandible for its required stable relationship by wiring the maxillary dentition or teeth to the dentition or teeth of the mandible through a dental occlusal splint, and then rotating the entire maxillary/mandibular complex upward until it abuts with the stable facial skeleton above. Unfortunately, the mandible itself is inherently unstable due to its rotational and translational relationship to two highly mobile joints (temporomandibular joints or TMJs). Stability of the mandible is attempted by manually placing the mandibular condyles (joint heads of the mandible) into a specific location within the joint space of the skull base (TMJ fossa).
The relation of the mandible when the mandibular condyles are in the most posterior superior unrestrained positions in the temporal bone glenoid fossa is known as Centric Relation (CR). With the mandible in CR (held manually typically by an assistant), the mandible is rotated with the attached maxillary segment to relate the osteotomized maxilla or loose dentate skeleton to the remaining facial skeleton using an “estimated” centric relation. The complex of bone and teeth are manually held in this position while the maxillary skeletal segment is fixated (wires/plates/screws) to the uncut facial skeleton. The entire process can be wrought with errors and problems.
In an anesthetized supine (lying on one's back) patient, the TMJ joints are lax and precise joint position is difficult to determine. Asymmetric positioning of the mandible can easily occur with only one of the TMJs in CR. Many patients undergoing orthognathic surgery have abnormal or dysplastic or absent TMJs making centric relation determinations difficult or impossible. Because CR relationships are determined manually (by feel only; the joint spaces are not visualized directly) the technique is very susceptible to error. This susceptibility is exacerbated by the fact that the CR position needs to be manually maintained for an extended time period intra-operatively while applying fixation to the maxilla in its new position. Shifting of the hand while holding the mandible, even slightly, can dramatically alter CR positioning. In addition, CR positioning of the mandible/maxillary complex also has no determination in the final vertical positioning of the maxilla. Final vertical placement of the osteotomized dentate skeletal segment of the maxilla is done in an entirely subjective fashion based on the surgeon's clinical determination in an anesthetized, supine, and facially swollen patient.
When a two jaw surgery (upper and lower, bimaxillary, double jaw) is performed, the maxilla is initially repositioned through the method described above. Next, the lower jaw or mandible is cut and repositioned based on the new maxillary position. This procedure is complicated by all of the problems related above with single jaw surgery, then compounded with the addition of the second jaw.
As an example, U.S. Pat. No. 6,726,479 and U.S. Pub. Appl. No. 2004/0166469 to Tremont disclose a technique utilizing a modified RED I device (KLS Martin, L.P., Jacksonville, Fla.) intra-operatively in order to determine skeletal relationships. Through a series of out rigging devices, an external bite is registered on a halo and compared to planned surgical changes. The halo is an externally mounted neurosurgical halo device which is very bulky and risks brain perforation with penetrating scalp pins. The registration bite with the RED I device can slip or torque easily, completely eliminating all accuracy. The halo itself is not completely rigid and can slip or torque easily, completely eliminating all accuracy. The device is expensive and impractical for intra-operative use in traditional orthognathic surgery.
U.S. Pat. No. 4,639,220 to Nara discloses a complicated technique utilizing a bulky, external halo frame similar to that of the Tremont patent (U.S. Pat. No. 6,726,479). The device described by Nara is complicated and is deficient for at least the same reasons as Tremont, discussed herein above.
As a further example, an article by Perkins et al., (Perkins, S., et. al.: “A Modified Boley Gauge for Accurate Measurement During Maxillary Osteotomies”. J Oral Maxillofac Surg 50:1018-1019, 1992) discloses a modified Boley gauge (Walter Lorenz) where a caliper is attached to a K-wire drilled into the skull of the patient intra-operatively. Changes in jaw position during surgery are measured, indicating change from original positions. The method described in the article by Perkins et al. is deficient because it only measures changes in dental positions. Furthermore, a minimal movement or torque of the long external wire required by the method of Perkins et al., completely eliminates accuracy of all measurements involved.
It would be desirable to have a simplified apparatus, system, and method for positioning a skeletal structure during orthognathic surgery, wherein disadvantages of the prior art are overcome by eliminating a dependency on Centric Relation (CR) for dentate skeletal repositioning.